Numerous materials, known as superconducting materials, are poor conductors when they are not in the superconducting state. In order for such materials to be in a superconducting state, three conditions must be satisfied:
1. The material must be at a temperature below a critical temperature. PA1 2. The density of current flow through the material must be less than a critical magnitude. PA1 3. The magnetic field associated with the material during current flow therethrough must be less than a critical magnitude. PA1 Nield & Mawardi, "Characteristics of Very High Currently Capacity Superconducting Switches", Proceedings of the IEEE, Vol. 53, No. 5, May 1965, page 523; PA1 Humphreys, D. R., et al, "Progress Toward a Superconducting Opening Switch," Digest of Technical Papers, Sixth IEEE Pulsed Power Conference, Library of Congress Cat No. 87-83052, IEEE Cat. No. 87CH2522-1, 1987; PA1 Tidman, D. A. and Thio, Y. C., "A Superconducting Opening Switch System," Technical Note 87-6, GT-Devices, Inc., 5705A General Washington Drive, Alexandria VA 22312, Aug. 12, 1987; PA1 Dronov, A. S. Ignatov, V. Y., and Misyulin, A. V., "Performance Study of Inductive Output Cryotronic Converters," IEEE Transactions on Magnetics, Vol. MAG-15, No. 1, January 1979.
If any of these conditions is not satisfied, the material will not be in a zero resistance state. The critical values for each of these conditions depend upon the material and the manner in which the material is processed.
Numerous switches have been proposed and created for switching a circuit which includes superconducting material. Most of these switches involve one or more of the conditions set forth above.
For example, U.S. Pat. No. 4,602,231 discloses a superconductive wire having a plurality of normal conductive stabilizing segments thereon. A heater is provided which raises the temperature of the superconductive material above its critical temperature to open the switch.
U.S. Pat. No. 4,754,384 discloses apparatus comprising superconductive material having a transition temperature Tc. The apparatus has a plurality of sections. During operation at least one section is maintained at a temperature below the transition temperature. This patent also discloses a switching operation in which a section is superconductive if the current therethrough is less than the critical current.
U.S. Pat. No. 3,800,256 discloses a superconductive switching apparatus in which the temperature of the switch is controlled for operation of the switch.
U.S. Pat. No. 3,768,053 discloses a superconductive switch which changes from a superconductive state to a normal electrically conductive state by changing its intrinsic magnetic field.
U.S. Pat. No. 3,686,458 discloses a switch which has a superconductive element which passes from a superconductive state to a conductor state by application of a pulse of an intense magnetic field.
U.S. Pat. No. 4,336,523 discloses a superconductor switching device in which a magnetizable element is arranged so that a magnetic field surrounds the superconductor. The conductivity of the superconductor is a function of the magnetic field surrounding the conductor.
Patent 3,384,762 pertains to cryogenic switching system for power transmission lines.
Other publications pertaining to superconducting switching are:
It is an object of this invention to provide means and a method for rapidly and effectively switching current flow through a body of superconductive material.
Another object of this invention is to provide switch means and method which can be employed with respect to a superconductor body of any physical size.
Another object of this invention is to provide such means and method which is compact and relatively low cost.
Other objects and advantages of this invention reside in the circuitry and the elements thereof, the combination thereof, and the method and mode of operation, as will become more apparent from the following description.